Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-08-15
2002-06-25
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S332800, C525S332900, C525S333100, C525S333200, C525S339000
Reexamination Certificate
active
06410657
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for the hydrogenation of a conjugated diene polymer, and more particularly, to the method for the selective hydrogenation of the unsaturated double bonds of conjugated diene polymer or copolymer using lithium hydride (LiH) as a reducing agent, so prepared from the reaction between organolithium compound and hydrogen, and an organotitanium compound in solution as the main catalyst, so as to improve its weatherability and oxidation resistance; thus representing an extremely high hydrogenation yield with remarkable hydrogenation reproducibility and selectivity.
DESCRIPTION OF THE RELATED ART
A conjugated diene homopolymer (e.g., 1,3-butadiene or isoprene) or a copolymer, so prepared via the reaction between a conjugated diene monomer and a vinyl aromatic monomer (e.g., styrene, etc.), is being widely used as an elastomer.
These polymers having the double bonds in their internal chain may be vulcanized but these double bonds may adversely cause the poor weatherability and the poor oxidation resistance of polymer.
Meantime, some block copolymers, so prepared via the reaction between a conjugated diene monomer and vinyl aromatic monomer, are being widely used as a modifier for transparent impact-resistant resin or polyolefin and polystyrene resin.
The polymers containing the olefinic unsaturated double bonds can be effectively used through a vulcanization process of the unsaturated double bonds but these double bonds raises some adverse drawbacks associated with a heat resistance, an oxidation resistance and weatherability.
Under the above circumstances, these polymers need to be used within limited scope of application, while not being exposed to the external environment. In an effort to improve the weatherability and oxidation resistance of polymers having the unsaturated double bonds, a process for partially or completely hydrogenating the double bonds in the polymers may, be generally adopted.
Several methods intended for the hydrogenation of the olefinic double bonds of polymer have been reported, which are largely classified by the following two methods.
The first method is to use a heterogeneous catalyst, and the second method is to use a homogenous catalyst such as Zeigler catalyst or an organometallic compound such as rhodium or titanium.
The hydrogenation method using a heterogeneous catalyst is performed in such a manner that olefinic polymer dissolved in a suitable solvent is contacted with hydrogen in the presence of a heterogeneous catalyst but such contact between reactants and catalyst is not easily made available due to some factors such as the steric hindrance of polymer and relatively high viscosity. Furthermore, once hydrogenation is successfully achieved due to strong adsorption of both the polymer and catalyst, their not easily detachable bonding characteristics make other unhydrogenated polymers extremely difficult to reach the active site of catalyst. To hydrogenate the unsaturated double bonds of polymer completely, excessive amount of catalyst should be required under severe reaction conditions of high temperature and pressure. As a result, the decomposition and gelation of polymer may be occasionally occurred.
Moreover, under the above severe reaction conditions, the selective hydrogenation of olefinic polymer is extremely difficult in that in the case of a copolymer, so prepared from a conjugated diene monomer and vinyl aromatic monomer, the hydrogenation of double bonds in an aromatic compound is simultaneously performed.
Furthermore, the physical separation of catalyst from a hydrogenated polymer solution is extremely difficult; in the case of a certain heterogeneous catalyst, its complete removal is impossible due to its strong adsorption with a polymer.
By contrast, the hydrogenation method using a homogeneous catalyst is more advantageous than using heterogeneous catalyst, since the catalytic activity is high and a high degree of yield can be expected under a mild condition such as a low temperature and pressure.
In addition, under an appropriate hydrogenation condition, the selective hydrogenation of olefinic double bonds only may be performed except for aromatic one from the chains of copolymer, so prepared from the reaction between a vinyl aromatic hydrocarbon and a conjugated diene.
Nonetheless, the method for hydrogenating the double bonds of a conjugated diene polymer using a homogeneous catalyst has recognized some disadvantages in that a) the stability of a catalyst itself is low, b) the separation of a catalyst decomposed from a hydrogenated polymer is extremely difficult, and c) after hydrogenation, the microstructure of polymer may be adversely affected.
Meantime, several methods to selectively hydrogenate the unsaturated double bonds of. conjugated diene polymer have been disclosed as set forth hereunder.
The U.S. Pat. Nos. 3,494,942, 3,670,054 and 3,700,633 have disclosed a method for using some well-known suitable catalysts containing the metals belong to 8, 9 and 10 groups or a precursor of catalyst, so as to hydrogenate and/or selectively hydrogenate a polymer containing the unsaturated double bonds of ethylene and a copolymer containing the unsaturated double bonds of both aromatic compound and ethylene.
From the above-mentioned patents, the catalyst is prepared by mixing some metals belonging to 9, 10 groups (especially, nickel or cobalt compound) with a suitable reducing agents such as aluminum alkyl. Besides, the prior art indicates that from the periodic table of the elements, some metals belonging to 1, 2 and 13 groups (especially, lithium, magnesium and aluminum alkyl or metal hydrides) are effectively used as reducing agents. Hence, some metals belonging to 1, 2 and 13 groups and some reducing agents belonging to 8, 9 and 10 groups are mixed in the molar ratio of 0.1:1~20:1, more preferably in the range of 1:1~10:1.
The U.S. Pat. No. 4,501,857 has disclosed a selective hydrogenation of unsaturated. double bonds in a conjugated diene polymer in the presence of (A) at least one bis-(cyclopentadienyl)titanium compound and (B) at least one hydrocarbon lithium compound.
Further, the U.S. Pat. No. 4,980,421 has disclosed a similar hydrogenation effect using either a direct use of a alcoholic or a phenolic compound or a reaction mixture between an organolithium compound and a alcoholic or a phenolic compound, with bis-(cyclopentadienyl)titanium compound as a main catalyst. Hence, even though a small amount of catalyst is used not to adversely affect the stability of polymer to be hydrogenated, its catalytic activity is quite effective.
The U.S. Pat. No. 4,673,714 has disclosed a process for selectively hydrogenating unsaturated double bonds of the diene units of a conjugated diene polymer and copolymer in the presence of bis-(cyclopentadienyl)titanium compound but in the absence of alkyl lithium compounds. The detailed example of such titanium compound includes a bis-(cyclopentadienyl)titanium diaryl compound, while the catalyst system is characterized by the non-use of a hydrocarbon lithium compound.
Further, the U.S. Pat. No. 5,039,755 has disclosed a process for the hydrogenation of a conjugated diene polymer which was made by polymerizing or copolymerizing at least one conjugated diene monomer with an organo alkali metal as a polymerization initiator in a suitable solvent, thereby creating a living polymer and terminating the polymerization by the addition of hydrogen and effecting selective hydrogenation of the unsaturated double bonds in the conjugated diene units of the terminated polymer by contacting the polymer in the presence of (C
5
H
5
)
2
TiR
2
(R=arylalkyl group) catalyst.
The U.S. Pat. No. 5,242,986 has disclosed that the double bonds in the conjugated diene units of styrene-butadiene-isoprene copolymer may be selectively hydrogenated using a specific titanocene compound and a reducing agent.
Further, the U.S. Pat. No. 5,583,185 has disclosed a method for hydrogenating the double bonds of conjugated diene units of polymer using Cp
2
Ti(PhOR)
2
(wherei
Hwang Jin Man
Kim Hoo Chae
Kim Jae Yun
Ko Young Hoon
Davidson Davidson & Kappel LLC
Korea Kumho Petrochemical Co., LTD
Lipman Bernard
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